U.S. Pat. No. 3,868,194 discloses an expandable articulated tandem roller in which both rolls can be steered. As there shown, however, only one roll at a time can be steered, whether merely to change direction of the machine or to expand or contract it. In particular, only the forward roll is steered, the trailing roll being locked in a "straight ahead" position. Width adjustment, especially, requires rather substantial time and effort, even with a skilled operator, since one and then the other roll must be separately turned several times and the machine largely halted between each. Furthermore, turning either roll while the machine is stationary is often apt to "tear" the mat, the chances of which are greatly reduced if the machine is moving when either roll is turned. Hence the chief object of the present invention is to provide a system and controls by which both rolls of a machine of the kind concerned can be turned simultaneously and while moving, whether for steering or width adjustment.